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Climate Change Bodes Poorly for Fish/Hydropower by Mike O'Bryant Columbia Basin Bulletin - November 22, 2002

Average temperatures will increase and snowpack in the Cascade Mountains will decline by up to 50 percent by mid-century, causing decreased summer and autumn stream flows in the Columbia River Basin, according to a draft report sponsored by the U.S. Department of Energy that will appear in the next edition of the journal Climatic Change.

While the report looks at the impacts of global warming across much of the West, a section by researchers in the Department of Civil and Environmental Engineering at the University of Washington focused solely on the Columbia River Basin.

That analysis predicted temperature and rainfall changes during three consecutive periods this century, projecting a 1.3 degree Centigrade increase in average temperature during the period 2040 to 2069, and an increase in winter precipitation during that period of 5 percent. However, by then, much of that winter precipitation will fall as rain and will not contribute to the winter snowpack that those who live in the basin rely on to produce energy and flows for endangered salmon populations. The basin can expect increased winter river flows, but decreased summer and autumn flows, the studied determined.

The study also considered how policy makers and river operators can resolve the tensions between power production and salmon flows, but the problem is that the Northwest can't have both, according to Dennis Lettenmaier, a professor of civil and environmental engineering at the University of Washington. He said water can be stored to generate electricity in the summer and fall, or it can be used to boost flows for salmon, but not both.

"The problem is you basically can't resolve that trade-off," said Lettenmaier.

The researchers found that the changes in temperature, precipitation and snowpack will affect all aspects of river use, including flood control, navigation, irrigation, power and salmon recovery and so they looked at several alternative operating policies for their potential to mitigate the changes, according to the report.

"In general, the combined use of an earlier refill target with greater storage allocations for in-stream flow targets was capable of mitigating most of the negative impacts, but only with severe losses of firm hydropower production," the report said. Those losses amount to 9 percent for the period 2010-2039, and 15 percent for each period 2040-2069 and 2070-2098. In general, power production will shift from summer and fall to winter and spring.

During those same periods, the report said temperature will increase by 0.5 degrees Centigrade, 1.3 degrees and 2.1 degrees respectively, while winter precipitation will decrease by 3 percent in the first period, 2010-2039, but increase by 5 percent during the period 2040-2069 and by 1 percent in the period 2070-2098.

Although researchers determined that the region's agencies could make some adjustments to prepare for the changes, including to flood control regimes, they also determined that the Northwest can expect "worsening of the extremes in climate," which could affect areas downstream that are vulnerable to flooding.

"The higher winter inflows associated with the seasonality shifts necessitate the continuation of present flood control policies despite the decreased ability of the system to replenish current evacuations in the spring," the report concluded. "The lower summer flows exacerbate the problems related to reduced refill by increasing drafts for instream flow targets. The lower resulting storage at the end of summer diminishes the ability of the system to meet present firm power production (hydropower 'safe yield') during the winter, before major precipitation cycles begin."

The full study, which was generated by the Accelerated Climate Prediction Initiative, included researchers from institutions including Scripps, the University of Washington, the Energy Department and the U.S. Geological Survey.

Globally, the study predicted annual average temperatures will rise 1.65 degrees Fahrenheit by 2050. That is lower than temperature increases predicted for the Northwest due to the Pacific Ocean's effects on Northwest climate. The ocean absorbs more of the heat.

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Northwest: report